The present invention relates in general to displays, and in particular, to field emission displays.
The current standard for flat panel display performance is the active matrix liquid crystal display (LCD). However, field emission display (FED) technology has the potential to unseat the LCD, primarily because of its lower cost of manufacturing.
Field emission displays are based on the emission of electrons from cold cathodes and the cathodoluminescent generation of light to produce video images similar to a cathode ray tube (CRT). A field emission display is an emissive display similar to a CRT in many ways. The major difference is the type and number of electron emitters. The electron guns in a CRT produce electrons by thermionic emission from a cathode (see FIG. 1). CRTs have one or several electron guns depending on the configuration of the electron scanning system. The extracted electrons are focused by the electron gun and while the electrons are accelerated towards the viewing screen, electromagnetic deflection coils are used to scan the electron beam across the phosphor coated faceplate. This requires a large distance between the deflection coils and faceplate. The larger the CRT viewing area, the greater the depth required to scan the beam.
FIG. 2 illustrates a typical FED having a plurality of electron emitters or cathodes 202 associated with each pixel on the viewing screen 201. This eliminates the need for the electromagnetic deflection coils for steering the individual electron beams. As a result, an FED is much thinner than a CRT. Furthermore, because of the placement of the emitters in an addressable matrix, an FED does not suffer from traditional non-linearity and pin cushion effects associated with a CRT.
Nevertheless, FEDs also suffer from disadvantages inherent in the matrix addressable design used to implement the FED design. FEDs require many electron emitting cathodes which are matrix addressed and must all be very uniform and of a very high density in location. Essentially there is a need for an individual field emitter for each and every pixel within a desired display. For high resolution and/or large displays, a very high number of such efficient cathodes is then required. To produce such a cathode structure, extremely complex semiconductor manufacturing processes are required to produce a high number of Spindt-like emitters, while the easier to manufacture flat cathodes are difficult to produce with high densities.
Therefore, there is a need in the art for an improved FED.
The present invention addresses some of the problems associated with matrix addressable FEDs by reducing the number of cathodes, or field emitters, through the use of beam forming and deflection techniques as similarly used in CRTs. Because fewer cathodes are required, the cathode structure will be easier to fabricate. With the use of beam forming and deflection, a high number of cathodes is not required. Furthermore, beam forming and deflection techniques alleviate the requirement that the field emission from the cathode structure be of a high density. Moreover, within any one particular cathode, as field emission sites decay, the display will remain operable since other field emission sites within the particular cathode will continue to provide the requisite electron beam.
A plurality of cathodes will comprise a cathode structure. For each cathode, an electron beam focusing and deflection structure will focus electrons emitted from each cathode and provide a deflection function similar to that utilized within a CRT. A particular cathode will be able to scan a plurality of pixels on the display screen. Software will be utilized to eliminate the overlapping of the beams so that the images produced by each of the cathodes combine to form the overall image on the display.
Any type of field emission cathode may be utilized, including thin films, Spindt devices, flat cathodes, edge emitters, surface conduction electron emitters, etc.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention.